The invention relates, in general, to a pallet container and more particularly to a pallet container of a type having a thin-walled rigid inner receptacle, preferably made from thermoplastic material for the storage and transport of liquid or free-flowing goods, wherein the plastic container is closely surrounded by an outer cage jacket as a supporting casing for the plastic container and a bottom pallet on which the thermoplastic receptacle is supported and which is firmly secured to the supporting casing.
Pallet containers of the type having a support jacket such as for example a wire cage jacket type or a cage jacket with horizontal and vertical bars are generally known in the prior art; e.g. from U.S. Pat. No. 4,676,373 (Schn./W).
The cage jackets in the pallet containers of the prior art are secured to the bottom pallet, which may be configured as a flat pallet from plastic or wood, or as a steel bar frame and is usually realized by fastening means such as for example, screws, brackets, clamps, clasps or claws that engage the lower horizontally surrounding cage bars. These fasteners are usually nailed, riveted, pinned screwed or welded to the upper plate or the upper outer edge of the pallet. In case where the pallet container has a support jacket of the bar cage jacket type, the cage bars can be configured as open or closed profiles having round cross section or rectangular cross section.
For industrial use, the pallet containers have to pass an official approval inspection and meet certain quality criteria. For example, the filled pallet containers have to undergo interior pressure tests and drop tests from specific heights, which are also conducted at extremely low temperatures (−20° C.). The worst case drop is a diagonal drop onto the lower pallet end side, which carries the bottom outlet valve of the inner plastic receptacle.
As has been shown in such drop tests, the inner plastic receptacle tends to shift relative to the bottom pallet during ground impact. Through the kinetic impact energy, especially at the impact end wall, the bars become severely deformed and in neighboring lateral peripheral regions are partly torn from the bottom pallet. The securement of the lower rim of the cage jacket to the bottom pallet thus is a crucial problem area. Since the attachment of the cage jacket is provided only at a few areas, the cage jacket, especially when a bar cage is involved, is deformed very unevenly and warps, whereby the thin-walled plastic receptacle can be damaged by torn off cage parts.
Pallet containers or combination-IBCs (IBC=Intermediate Bulk Container) of the type involved here are used for transporting liquids. Preferably, they usually have a filling volume of 1000 liters and consist of a pallet, a cage jacket, which is attached to the bottom pallet, and an inner receptacle made from PE-HD, which is firmly surrounded by the cage jacket, and which has an upper fill opening and a lower outlet fitting.
Upon diagonal drop testing at the lower critical pallet end face (the area where the outlet fitting of the inner container is disposed), the inner container with the liquid content has the tendency of lateral slipping and shifting in the direction of the forward or lower cage wall. The surge forces of the content and the thrust force of the inner container must be absorbed primarily by the forward cage wall. As a result of the ground impact of a filled pallet container during the diagonal drop test quite significant elastic and plastic, i.e. permanent, deformations are incurred; which lead to catastrophic deformations and damage to the inner container, when the cage jacket and pallet have insufficient strength. The area around the outlet fitting is hereby predominantly at risk.
The test conditions during drop testing include that the inner container must be absolutely tight, without leakage of any content from the outlet fitting or from the overstressed stretching areas of the inner plastic container, and that the pallet container is still maneuverable, i.e. that it can be picked up by a fork lift and be able to be transported. These are essential preconditions for the pallet container to receive official approval for use with hazardous liquid contents.